IPSC is an IP subnet calculator. There is a command line version, ipsc, and a GNOME version, gipsc.
You give the network class and subnet bits and you get back the maximum number of subnets, maximum number of hosts per subnet, a bitmap showing the breakdown of network bits, subnet bits, host bits, the decimal and hexadecimal class netmask, the decimal and hexadecimal subnet mask, and more.
Tucows, Inc has graciously donated a copy of this software to the Internet Archive's Tucows Software Archive for long term preservation and access. Please check the Tucows website for all current versions of the software.